Plaice
Photo: Sue Scott
Dab
Photo: Sue Scott
Flounder
Photo: Sue Scott
Sole
Photo: Sue Scott
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On one of my frequent, long train journeys, I overheard a mum explaining to her small child that flatfish were flat because of the
great weight of water pressing down on them in the great depths they lived in. I'll never know whether she really believed this, but I remember thinking what a shame to be filling this small person's head with rubbish when the real story is even more fantastic, and would have entertained said child for much longer!
Flatfish actually begin life as normal-looking, upright-swimming fish larvae, but after a few weeks feeding in the plankton, weird things start happening. One side of the tiny fish's skull grows faster than the other, displacing one eye over the top of the head to join the other eye on the opposite side of the body. Its mouth becomes twisted and develops more on the eyeless side. The little fish, now with a rather grotesque face, starts swimming on its side, with eyes uppermost. At a centimetre or two long, it settles onto the sea bed, then lives its entire adult life lying on its blind side. Plaice, dabs, flounders, and lemon sole usually have eyes on the right side of the body, while other flatfish, including brill and turbot, are normally left-eyed.
Flatfish are great little movers, undulating through the water like miniature magic carpets, with a surprising turn of speed when required. But much of the time they lie almost invisible on the sea bed, in camouflage colours. Juvenile flatfish are almost see-through, but soon develop pigments on the upper side, in patterns that can be altered so that the fish exactly matches its background. (Imagine a flatfish jigsaw! Level of difficulty - mind-numbing). A favourite trick in public aquaria is to swap young flatfish between dark and light coloured sands, to see how quickly they change colour - usually only a minute or two. Flatfish also flip sand up over their bodies, to avoid showing a flatfish-shaped outline. Interestingly, an alarmed sole leaves the black tip of its pectoral fin showing after diving into the sand. This resembles the dorsal fin of the venomous weever, so may trick potential predators into leaving it alone.
Most flatfish hunt by sight, catching a wide range of smaller animals. Dab and lemon sole are expert at pouncing on mollusc siphons and worm heads, biting them off with their sharp teeth. Plaice have a special set of crushing teeth in the throat, enabling them to deal with whole molluscs, and they often come inshore at high tide to feed on cockle and mussel beds.
Not even his mum loves the ugly flatfish. Flatfish are not hot on parenting, so to ensure the next generation they spawn huge numbers of eggs, up to 150,000 in the case of the dab, half a million for the plaice, and up to two million for the flounder. The eggs and larvae drift with the water currents for a few weeks to several months, depending on species and water temperature. However, most of them get eaten in the open-water jungle of the summer plankton, only a tiny percentage surviving long enough to settle on the relative safety of the sea bed as miniature flatfish. So, that plaice you saw on your dive (or plate!) is one in a million, literally.
KNOWN HAUNTS
Plaice and dabs live mainly on sand, while flounders prefer muddier sea beds, and also live in estuaries and the lower reaches of rivers. Lemon sole can be found on rock as well as firm sand and mixed sea beds.
BEST PLACE TO SEE
All around Britain
LIKELY TO APPEAR
Present all year
DISTINGUISHING FEATURES
Oval or diamond-shaped flatfish with twisted faces. Plaice have obvious bright orange spots and rows of small bony protuberances on the head. Dabs often have very small orange spots, and have a pronounced curve in the lateral line where it runs around the pectoral fin. Flounders have bony tubercles along both sides where the fins meet the body. Lemon sole are often more brightly coloured, with patches of pink and yellow as well as duller colours.
SIZE
Plaice grow to 50-60cm (exceptionally 90cm), flounders to 50cm, dabs to 25cm (exceptionally 40cm), and lemon sole to 40cm (exceptionally 70cm).
